As a professional 3D artist, I'd like to chime in and express my hopes that some effort be made towards more robust documentation and learning materials in general. It has been easy to find feedback from the enthusiast community, but still is much harder to find learning resources to get me up to speed and produce professional quality results out of Terragen than with any other software package out there geared for professional post production/3D content creation that I've had to learn.
It's not because of lack of capability from the software, that is for sure. In the end, I'd love to have all the time in the world and learn the intricacies of creating fancy node networks, but I don't. And so while I'd love to use Terragen more often since I did spend money to purchase a full pro license, and a maintenance update (and now I'm due for another one), I end up creating more content in other packages because I know I can get it done. I also know Terragen would be more expedient for certain things, but I just have had a hard time finding great learning resources. Most of the tutorials are stale, and the documentation tends to suffer from lack of structure.
Anyways, I hope you'll find this feedback constructive.